In a mobile telecommunication network like a UMTS system, a primary station, for instance a Node B (or Base Station or eNB) communicates with at least one secondary station, for instance a User Equipment (UE or Mobile Station), by means of a plurality of channels. In order to transmit data to the primary station, or to receive data from the primary station, a secondary station needs to listen to signaling message on at least one control channel to know when to transmit or receive, and to know how to transmit or receive. Among the parameters used to determine how to communicate with the primary station, the secondary station needs for instance at least some of the following:
For downlink data transmissions, each such control signalling message may typically include at least some or all of the following:                Time-frequency resource allocation,        Number of MIMO (Multiple In Multiple Out) layers used,        Hybrid ARQ (Automatic ReQuest) process number,        Modulation and Coding Scheme for each layer,        New data indicator for each layer,        Redundancy version for each layer,        Precoding information for each layer,        UE identity,        Cyclic Redundancy Cycle.        
Usually, all these parameters are transmitted on a single control channel. However, for some applications, a semi persistent scheduling with a particular signaling is used. In accordance with semi persistent scheduling scheme, a resource is allocated for instance periodically (i.e. each subframe or each nth subframe) for a large period of time. This is used for instance for communication where repeated resources will be used, like Voice over IP. By using this semi persistent allocation, it is possible to fix some parameters of the future transmissions, for instance by higher layer signaling, and the required amount of signaling to be transmitted on the control channel is reduced. The transmission on higher layer has the drawback of being not as quick as the normal signaling. However, this is well adapted for semi persistent scheduling.
What still needs to be transmitted to the secondary station on the control channel is a message to activate or deactivate or modify a Semi Persistent Scheduling (SPS).
However, if this SPS message is missed or wrongly decoded, or received in error, this can lead to several problems, like collisions with another communication or corruption, leading to delays and errors.